1. Field of the Invention
The present invention relates to an apparatus for checking baggage with X-rays and particularly to a technique for correcting picture distortion in an X-ray baggage checking apparatus in which X-rays passed by and through baggage are detected by an X-ray detector constituted by a plurality of X-ray detecting elements arranged in an L-shape and a detection signal is displayed as a picture.
2. Description of the Prior Art
An X-ray baggage checking apparatus for checking baggage as to whether any dangerous object is hidden in the baggage or not by irradiating the baggage with X-rays, has been used in an airport, and so on. Conventionally, such an X-ray baggage checking apparatus has been arranged such that the two line sensors each constituted by a plurality of aligned X-ray detecting elements, for example, each compound of a phosphor for converting X-rays into light and a photodiode for converting light into an electric signal, are disposed in an L-shape at a portion above a baggage conveyer device, and two X-ray generating devices are provided respectively corresponding to the pair of line sensors so that information respectively obtained by the two sets each composed of one X-ray generating device and one line sensor are separately displayed as separate pictures.
In such an arrangement, however, there has been problems that not only two X-ray generating devices, two X-ray detectors, two picture processors, and two display devices are required to thereby make the X-ray baggage checking apparatus expensive but the entire area of a rectangular shape formed by the two L-shaped detectors with the two detectors as the adjacent two sides of the rectangular shape cannot be used as a checking range.
In order to solve those problems, a method has been proposed in which an X-ray detector is formed in a single L-shaped line sensor and a single X-ray tube device is provided so as to radiate X-rays with which the single L-shaped line sensor is irradiated to thereby make it possible to perform checking at any portion in the whole area defined by a baggage conveying surface of a conveyer device and the L-shaped line sensor (see FIG. 3).
In a method in which an object to be irradiated with X-rays and the X-rays passed by and through the object to be checked are taken out as information, basically, a projection image carried by X-rays radially spread from a point, that is, an X-ray tube focus, is obtained. That is conventionally, X-rays radiated from a single X-ray tube focus are detected by an X-ray detecting medium having a flat or smooth-curved surface. In this case, the obtained information is displayed as a uniformly continuous picture.
In such a picture obtained by radiation of X-rays from a single X-ray tube device onto a single L-shaped X-ray detector, however, unavoidable distortion is generated such that one part of the picture formed by the data obtained through the detecting elements on one side of a boundary, that is, a point of intersection between two lines forming the L-shape of the X-ray detector, is distorted relative to the other part of the same picture formed by the data obtained through the detecting elements on the other side of the above-mentioned boundary.